OBSERVATIONS ON THE ASSAY OF TELLURIDE ORES.
1023
INFLUENCE O F VOLUME O F SOLVENT.
(Solvent:
17" . - Citric Acid Solution.) Phosphoric acid (PzOd.
Per cent. 100 100
100 100
grams grams grams grams
soil soil soil soil
in 1000cc. 7 days., , , . , 0 . 0 2 2 8 7 in 500 cc. 7 days. , . , , , . 0.01999 in 1000 cc. 5 hours, , , . , 0.01807 h 5 0 0 cc. 5 hours., . . . . 0.01599
Potash (KzO). Per cent.
Lime (CaO). Per cent.
0.03818 0,03355 0.03958
0.2718
0.03089
0.228j
0 .j320
0.5210
In this table are given the same data as in the preceding, but they are arranged to more readily show the influence of the volunie of solvent. No detailed discussion of these data is necessary; a glance at the figures is sufficient to make apparent the only conclusion that can be reached, viz., that reducing the volume of solvent used, materially decreases the percentages of phosphoric acid and potash obtained. In the case of lime, the smaller volume extracted but one-half that taken out by the larger volume. Clearly the influence of volume of solvent is decidedly greater than that of the period of extraction. No doubt soils of a different character would not yield results that would fall exactly into line with those here recorded, that is, as to the effect of varying the period of extraction and the volume of the solvent on the amount of mineral matter dissolved, but the general trend would, we believe, be the same. It seems highly desirable that further data on this important question of available plant food should be obtained from widely different points and correlated with the field results. These analytical data should be, as far as is practicable, strictly comparable, and to this end it is evidently necessary that the details of the process as regards period of extraction and volume of solvent, should be carried out alike by all workers. There seems to be every reason for adherence, in these respects, to the time and volume as given by Dr. Dyer in his original account of the process. DOA~INION EXPERIMENTAL FARM, OTTAWA, CANADA.
SOME OBSERVATIONS ON THE ASSAY OF TELLURIDE ORES. BY GEORGEB O R R O W M A N . Received April 4, 1908.
Much has been written concerning the assaying of telluride gold and silver ores, yet the literature affords striking contradictions as well as statements unsupported b y experimental data. However, there seems t o be agreement in the opinion t h a t tellurium is the cause of serious irregularities. Mr. A. I,. Davis, in Tech. Quart., VoZ. X I I , sums up the situation a s follows: "As to the percentage of loss sustained in work, whether by scorification o r crucible method, many experiments carried out upon the foregoing lines indicate t o me that nothing definite can be
1024
GEORGE BORROWMAN.
laid down in regard to it. Every ore, every slag, every scarification, every cupel, let alone the tciiiperature a t which the assay is carried on, has some effect upon thc loss and tlicsc. make too many unknown quantities t o arrive a t any conclusion." It was the purpose of the writer in the work here recorded t o ascertain a few facts concerning thc effect of tellurium in the crucible assay for gold. The points investigated were : loss in the slag; loss in cupellation ; the effect of variation in temperature of fusion. The ore selected for the experiments was a high-grade telluride gathered from various parts of Colorado, rich in silver, gold and tellurium. With the sulphuric acid test it gave a w r y strong indication of the latter element and analysis showed the presence of IO.j per cent. chiefly as hessite and sylvanite. The gangue was silicious: consisting of quartz, feldspar and a little calcite. The ore had a reducing power of about I . j. The material was ground \rery finc, first through 1 2 0 mesh sieve, then in agate till all passed through bolting-cloth. In all the work 1/10A. 1' .' was taken for each assay, the samples being weighed out on a quantitative balance instead of on the usual pulp scales. All fusions were made in a muffle a t about I zooo excepting in Series No. 4 ; all the fluxes were passed through a 40-mesh sieve mixcd with the ore till thoroughly homogeneous. In short, the greatest carc was taken to eliminate all variations except the one studied. Experiments were first conducted to learn the influence of tellurium in carrying gold into the slag. Xr. C. H. Fulton, in THISJOURNAL, 2 0 , 586, records data to show that slag losses in telluride fusions are much greater than in ordinary gold ore crucible work. Messrs. Hillebraiid and Allen, Bulletin No. 253, U . S . Gcologicul Survey, find losses insignificant, and commenting 011 the work of Mr. Fulton suggest that his losses might have been due to the use of iron nails in the fusions. In the investigation of this point a serics of assays was first made on the raw ore, using the following charge: Ore
1/10
A. '1%.
Sodium bicarbonate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 g. Salt cover.
Another series was then made on ore from which the telluriuni had been removed. In removing it use was made of the fact t h a t nitric acid dissolves tellurium and silver in a telluride and leaves the gold in the residue. Each sample was boiled with nitric acid ( 1 . 2 7 ) till no further action wds apparent; the residue was washed and dried and fluxed under the same coriditions as niairitained in the first series. Enough silver
OBSERVATIONS ON THE ASS.4Y OF TELLURIDE ORES.
1025
was added to the de-tellurized series to replace what had been removed by the acid. The slags from each series were then carefully ground and assayed, using the following charge : Slag Litharge, . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Argols. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Salt cover
30 g. 2 g*
The results
The buttons from both the ores and slags were cupelled. are set down in the following tables: SERIESNo.
I.
OR. No. I 2
3 4
O E .gold per ton..
'Mg. gold found.
Av . . . , . .
16.14 16.18 16.18 1-6.-. __ 23 16.18
161.4 161.8 161.8 162.3 161.8
SERIESNo. Mg. gold found.
I
1 6 .IO 16.16 16.20 1-_ 6.11 16.14
2
3 4
None
',
' I
"
2.
Ore.
No.
Slag. Gold found.
0 2 . gold
per ton.
I G I .MI 161,60 162.0 161.I O 161.4
Slag. Gold found.
Trace None Trace None
Av . . . . . . From the above data it is obvious that the influence of tellurium in carrying gold into the slag is very slight, if there is a n y ; the amount recovered was in no case weighable. The effect of tellurium in cupellation was next investigated, and incidentally the functions of litharge in the fusion. On the assumption t h a t the tellurium in a crucible charge is oxidized by the litharge and carried into the slag, a series of charges was made up varying this constitutent from 90 to 180 grams. Theoretically the amount of tellurium carried into the button as a lead alloy should be in inverse ratio to the amount of litharge in the fusion. A series of four samples was made in duplicate. The buttons of one series were dissolved in nitric acid and the tellurium determined by precipitating it in hydrochloric acid solution with sulphur dioxide. The other series was cupelled for gold. The two duplicates are considered as one series, i. e., No. 3. SERIESNo. 3. No.
Grams. PbO in charge.
Mg. Te i n button.
lost
I
90
2
I20
287 ' 5
3 4
150
298.9
I80 Average.. . . ,
Mg. gold found.
176.8
.. , ..................
~
1 6 .I O 16.24 16.18 16.15 16.17
02.
gold per ton.
161 .oo 162.24 161.80 161.50 __ 161.70
XI1 of tlic licatls ol' the a h v c sc.rics were frosted, showing the presence of tclluritiiii, riot nitlistmicling tlic great excess of litharge in the fusion. It \\-oultl tlicn bee111 tliat litharge in reasonable amount is inadequate to slag off a11 1111. telluriuni iii t1:is ore. 'l'hc loss of gold, however, was inconsitlerablc, the avc~ragcol tlie series yarying but 0.01 mg. from the avoragc ( i f Svrivs So. I in wliicli the tclluriuni had been removed previous to fusioii. 'I'licse results are a t variance with published statements regarding tcllui.iiiiii ill ciipelhtioii. Nessrs. '1'. J. I.:ager and UT. W. Welch, Iion.c\.cr, I'ountl tliat no loss occurretl in the presence of the element u p to, i o pc'r cent. '1'11~ :linotints in tlic above cspcrirnent are many times that. .I be:ttl Troiii ail assa?.. tliil)lic:ttc, of No. I in the above series which was also t h e s t i i v :is [!iosc of Series No. 2 , was tested quantitatively for tcll~Liriiini a i i t l 6.0 iiig. \ w r c f o i i n t l : so that it may be present even in the lieat1 i i i ccJiisitlci.;il)le:iniouiit \vitliout there being more than a negligible loss ol :()I(!. ,.l h c \vork \\.as concluded u i t h sonic experiments to learn the effect of variation oi tmipcraturc o f iusion on gold recovered and the amount of telluriiim carriid into thc. h i t t o n . Some assayers recommend an extrtniely high tempc.raturc. 3Ir. I
